> For the complete documentation index, see [llms.txt](https://swatplus.gitbook.io/io-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://swatplus.gitbook.io/io-docs/introduction-1/hydrology/hydrology.hyd/perco.md).

# perco

The percolation coefficient is input to limit percolation from the bottom soil layer due to an impermeable layer or high water table. Since percolation can be a slow process, that can occur over days or weeks, the percolation coefficient is non-linear and difficult to parameterize and calibrate. 

{% hint style="info" %}
A *perco* value of 0.0 does not allow any percolation from the soil and a value of 1.0 does not restrict percolation from the bottom soil layer.
{% endhint %}